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Species of Volvulella are distinguished externally from other small, shelled cephalaspideans by the pointed extension at the posterior end of the shell. They are usually considered to be related to the Retusidae but lack both radula and gizzard plates. Little is known of their biology and natural history other than they live in sand and sandy mud.

Volvulella and Rhizorus. Unfortunately many shelled opisthobranchs have been named on the basis of their shells alone, and this is a case in point. For the last 100 years there has been an on-going debate, unhappily still unresolved, over the names Volvulella Newton, 1891 [for Bulla acuminata Bruguiere, 1792] and Rhizorus Montfort, 1810 [for R. adelaidis Montfort, 1810] and whether they are synonyms. The shells certainly look the same but as they were described only on the shell it is very difficult. On top of that, Mediterranean and Nth American workers seem to prefer Volvulella while workers on the Nth Atlantic and Australian - New Zealand regions have opted for Rhizorus.

Thanks very much. There are not many people out there looking for live cephalaspidean bubble shells, so I welcome any photos I can get. Your reference to the Volvatella message gives me the chance to mention the somewhat similar shape of the shells in the sacoglossan Volvatella and the cephalaspidean Volvulella.

Unfortunately many shelled opisthobranchs have been named on the basis of their shells alone, and while the shells of Volvatella and Volvulella are easy to distinguish, there has been an on-going debate, unhappily still unresolved, over whether the names Volvulella Newton, 1891 [for Bulla acuminata Bruguiere, 1792] and Rhizorus Montfort, 1810 [for R. adelaidis Montfort, 1810] are synonyms. The shells certainly look the same but as they were described only on the shell it is very difficult to be sure. On top of that, Mediterranean and Nth American workers seem to prefer Volvulella while workers on the Nth Atlantic and Australian - New Zealand regions have opted for Rhizorus.

I have always preferred Rhizorus, as the older name, but have retained your usage of Volvulella in the hope of opening a discussion on the topic.